Pigment dispersion composition, display apparatus, and method of manufacturing the apparatus

Abstract: The pigment dispersion composition having a good dispersibility, a good transparence and an anti-coating properties, which contains 0.5 to 50 parts by weight of an inorganic pigment, at least one type of dispersant selected from the group consisting of a sodium salt, an ammonium salt and an amine salt of an acrylic resin, an acryl copolymer resin, a polycarbonic acid, a condensation product of aromatic formalin sulfonate, and water or a solvent miscible with water. Display apparatus, such as a cathode ray tube, with a coating of said pigment disfusion and method of manufacturing the apparatus.

Description: The present invention relates to a pigment dispersion composition having a good dispersibility and a good transparence, with such excellent anti-coating properties that the composition does not have an adverse influence on other materials, i.e. soaking into other coatings. The present invention further discloses a display apparatus such as a cathode ray tube and a method of manufacturing the apparatus. A color cathode ray tube is an example of a display apparatus for displaying an image by using emitting light from a phosphor layer. Conventionally, various methods for improving the contrast or color purity of such a display device have been proposed. For example, Jpn. Pat. Appln. KOKAI Publications Nos. 48-17263, 52-63060 and 64-7457 each disclose a method in which a pigment layer having the same color as that of the emitting color from the phosphor layer is provided between the face plate and the phosphor layer. Further, Jpn. Pat. Appln. KOKAI Publication No. 52-77578 discloses a method of forming a pigment layer by adding a pigment into a pre-coating solution before the phosphor layer is applied. Jpn. Pat. Appln. KOKAI Publications Nos. 53-69577 and 56-160746 each mention a method of embedding phosphor particles into a pigment layer which was made sticky. Jpn. Pat. Appln. KOKAI Publication No. 53-65654 discloses that a phosphor screen is formed by forming a pigment layer containing a binder in the inner surface of a panel and then applying a phosphor suspension containing a photo-sensitive binder on the pigment layer, thereafter exposing the suspension to light and developing. However, the above-described methods entail the below-described drawbacks, and therefore it is difficult to actually employ such a phosphor film having a pigment filter layer. First, the transparence of the pigment layer is insufficient, and the performance of the filter is poor, thus making it not possible to achieve good contrast properties. Second, the method involves a limited condition for work, and therefore defect-free filter layers cannot be constantly obtained. According to the method of manufacturing a phosphor screen disclosed in Jpn. Pat. Appln. KOKAI Publication No. 64-7457, the pigment layer is formed by the slurry method, and after a while, the phosphor layer is formed by further using the slurry method. As a result, the number of the steps involved is twice as many as a general method, and the production cost is increased. The present invention has been proposed in consideration of the drawbacks of the conventional techniques. The first object of the invention is to provide a pigment dispersion composition having a good dispersibility and a good transparence, with such excellent anti-coating properties that the liquid composition does not have an adverse influence on other materials, i.e. soaking into other coatings. The second object of the invention is to provide a display apparatus including a phosphor screen with an filter by using such pigment dispersion composition, the phosphor screen providing with a pigment layer having the same color as the emitting color from each phosphor layer, between the face plate and the phosphor layer, and having a good transparence, a good filter performance which means light emitted from phosphor can be transmitted through the filter while the other light can be absorbed in the filter, and contrast properties, which does not occur color contamination, so as to be excellent for practical use. The third object of the invention is to provide a method of manufacturing a display apparatus including a phosphor screen with a filter, by using such pigment dispersion composition, having a good transparence, a good filter performance, and contrast properties, which does not occur color contamination, easily at a low cost. The pigment dispersion composition of the present invention has a good dispersibility and anti-coating properties. A high dispersibility indicates good filter properties, and an excess pigment dispersion composition which is applied to an undesired part in the patterning step can be easily removed, and hardly remains at such a part. When the anti-coating properties are good, high filter properties can be obtained for the following reason. That is, if a phosphor layer is formed on a film which was formed simply by coating the pigment dispersion composition, the pigment dispersion composition does not seep out into the phosphor layer. When the pigment dispersion composition is used in a display device, the display device of the present invention, having a brightness, contrast characteristics and color purities, which are all improved, can be obtained. Further, the pigment dispersion composition has good anti-coating properties, and therefore it is no need to add a photoresist, the treatment of the composition by exposing to light and development. Consequently, with the method of the present invention, another coating layer containing the photoresist can be formed on a coating layer of the pigment dispersion composition without the just mention treatment. Therefore, it only suffices that a patterning is performed on the photoresist-containing layer, so as to pattern the photoresist-containing layer together with the coating layer of the pigment dispersion composition. In the case where the photoresist-containing layer also contains phosphor, a phosphor layer can be formed by performing a development process and an exposure step once. Thus, according to the present invention, the manufacturing steps can be facilitated without deteriorating the filter effect of the pigment layer, or the light emitting efficiency of the phosphor layer. This invention can be more fully understood from the following detailed description when taken in conjunction with the accompanying drawings, in which: FIG. 1 is a schematic diagram showing an example of the display apparatus according to the present invention; and FIGS. 2A to 2G are diagrams showing some of the steps of an example of the manufacturing method for a phosphor screen of the display apparatus according to the present invention. The inventors of the present invention carried out studies for simplifying the manufacturing step for the display apparatus having a filter between the face plate and the phosphor, by only adding a step of coating the pigment dispersion composition, and performing the exposure/development step of the pigment layers at the same time with the phosphor layer after the application of the phosphor layer. Further, the inventors focused on the dispersant for the pigment dispersion composition used for forming the pigment layer, and studied the influence of the dispersant on patterning. The results of the studies were summarized in TABLE 1. In TABLE 1, the transparence is an evaluation of whether the pigment filter formed of a pigment layer has a sufficient transparence without scattering or not. In order to maintain the transparency, it is required that the diameter of the pigment particles be several hundred nanometers or less, preferably, several tens of nanometers, and the particles be dispersed uniformly in the filter layer, and which be maintained after the application. In the case where a high transparency is not maintained, the contrast and color purity are degraded due to scattering of light, even if there is an attempt of improving the contrast and color purity by using the pigment having the filter properties. The anti-overcoating properties are an evaluation of whether or not the pigment layer becomes defective due to the pigment layer melting into the phosphor slurry or part of the phosphor slurry mixed into the pigment layer, which may take place in the step for forming a pigment layer and forming a coating layer such as of phosphor slurry on the formed pigment layer. The underlayer adhesion property is an evaluation as to the antinomy in which the exposure part has sufficient adhesion properties, whereas the non-exposed part has sufficient removing properties, and thus the adhesion properties must be appropriate, during patterning by the exposure and development. According to the experiments of the present inventors, the pigment particles were prevented from agglomeration by using a suitable dispersant in the pigment composition, thus improving the transparence. Particularly, in the case where an anionic dispersant was used, it was confirmed that the anti-overcoat properties and the underlayer adhesion properties, which were the rest of the necessary characteristics, could be improved to a practical level at the same time. However, as shown in FIG. 1, in the case of Na salt, the anti-overcoat properties are somewhat poor, or in the case of NH 4 salt, the underlayer adhesion property in the non-exposed portion is poor. The conditions for work are limited. Better properties can be obtained when the dispersants are mixedly used. Based on the above results, the synergetic effect in the case where the dispersants were mixed in was examined. It was found that all of the above properties were improved in the case where the mixed ratio (anionic Na salt / anionic NH 4 salt) was in a preferable range of 7/3 to 10/0. It was also found with respect to the combination of a nonionic dispersant and an anionic NH 4 salt that all of the above properties were improved in the case where the mixed ratio (nonionic dispersant / anionic NH 4 salt) was in a preferable range of 1/30 to 1/300. The reason why the mixtures of dispersants exhibit good properties is as follows. That is, the anionic NH 4 salt becomes a coating film which is insoluble in water as NH 3 evaporates during the formation of the film, and the anionic Na salt does not evaporate during the formation of the film, and remains in the coating film as Na salt, rendering the coating film water-soluble. Therefore, the characteristics of the coating film with respect to water can be controlled by appropriately setting the mixed ratio at appropriate values. Further, the nonionic dispersant is highly soluble in water, and therefore with its addition to the anionic NH 4 salt in the application liquid in a small amount, the film which has been insoluble in water becomes somewhat soluble. The pigment dispersion composition according to the first embodiment of the present invention has been derived from the various studies of the inventors, and contains at least: i) 0.5 to 50 parts by weight of an inorganic pigment having a particle diameter of 10 to 200 nm; a dispersant; and water or a solvent miscible with water, characterized in that: said dispersant comprises a mixture of a sodium salt dispersant and an ammonium salt dispersant, or a mixture of an ammonium salt dispersant and nonionic dispersant, said sodium salt dispersant is selected from the group consisting of a sodium salt of an acrylic resin, a sodium salt of an acrylic copolymer resin, a sodium salt of a polycarboxylic acid, and a sodium salt of a condensation product of aromatic sulfonate and formalin, and said ammonium salt dispersant is selected from the group consisting of an ammonium salt of an acrylic resin, an ammonium salt of an acrylic copolymer resin, an ammonium salt of a polycarboxylic acid, and an ammonium salt of a condensation product of aromatic sulfonate and formalin. If the grain diameter is less than 10 nm, the agglomeration between pigment particles tends to become too strong, and the particles may not easily be dispersed, whereas if the particle diameter exceeds 200 nm, the transparence tends to be degraded to an insufficient level, lowering the filter properties. The content of the inorganic pigment should preferably be 3 to 35 wt%. If the content exceeds 35 wt%, the viscosity of the pigment dispersion composition increases, it tends to be difficult to apply the composition uniformly. If the content is less than 3 wt%, the color tends to be weak, and the filter properties may be degraded. The content of the dispersant should preferably be in a range of 0.5 to 20 wt%. If the content is less than 0.5 wt%, the dispersion of the pigment tends to become insufficient, and the particle diameter may become large, deteriorating the filter properties, whereas if the content exceeds 20 wt%, the underlayer adhesion properties tends to be enhanced, degrading the patterning quality. The content of the dispersant with respect to the inorganic pigment should preferably be in a range of 2 to 30 wt%. If the content is less than 2 wt%, the dispersion of the pigment tends to become insufficient, and the particle diameter may become large, deteriorating the filter properties, whereas if the content exceeds 30 wt%, the underlayer adhesion properties tend to be enhanced, degrading the patterning quality. Examples of the solvent miscible with water are: methyl alcohol, ethyl alcohol, isopropyl alcohol, glycolethers such as ethyleneglycol monobutylether and propyleneglycol monomethylether, polyhydric alcohols, N-methylpyrrolidone 2-pyrrolidone, and N-N-dimethylformamide. As a sodium salt dispersant there can be used an Na salt of an acrylic agent, an acryl-styrene agent, an acryl copolymer, a polycarbonic acid, or a condensation product of naphthalene sulfonic acid and formalin. A preferable sodium salt dispersant is an Na salt of an acryl copolymer. Specific examples of the anionic Na salt dispersant are: Dispeck N-40 (Allied Colloid Co.) as an acrylic agent; Demol EP (Kao) or Poiz 520 (Kao) as a high-polymer polycarbonic acid; Demol N (Kao) as a condensation product of naphthalene sulfonic acid and formalin; Demol MS (Kao) as a condensation product of specific aromatic sulfonic acid and formalin; and Elenone No. 19N as an octylphosphatemonoethanol amine acid. Of all, the most effective agent is an acryl copolymer, and a specific example thereof is Dispeck G-40. As an anionic NH 4 salt dispersant there can be used an ammonium salt of an acrylic agent, an acryl-styrene agent, an acryl copolymer, a polycarbonic acid, and a polyoxyethylene alkylether sulfate. Specific examples of the anionic NH 4 salt dispersant are: Dispeck A-40 (Alllied Colloid Co.) as an acrylic agent; Discoat N-14 (Dai-ichi Kogyo Seiyaku Co., Ltd.) as a high-molecular polycarbonic acid type; Hitenor 08 (Dai-ichi Kogyo Seiyaku Co., Ltd.) as polyoxyethylene alkylethersulfate; and Lomar PWA (Sunnobco Co., Ltd.) as a condensed naphthalenesulfonic acid. Of all, the most effective agent is an acryl copolymer, for example, Dispec GA-40 (Allied Colloid Co.). Examples of the nonionic dispersant which can be used in the pigment dispersion composition of the present invention are: polyoxyethylene laurylether, polyoxyethylene derivative, polyoxyalkylene alkylether, polyoxyethylene nonylphenylether and polyoxyethylene sorbitanmonolaurate. Specific examples thereof are Noigen EA-140 (Dai-ichi Kogyo Seiyaku), Emulgen 106 (Kao) and Leodol TW-L120 (Kao). Pigments using for the present invention can be selected from an inorganic and an organic pigments. It is preferably selected that pigments which can be dispersed uniformly in a filter layer of a phosphor screen and make the filter layer having good transparency. Specific examples are iron oxide pigments such as SICOTRANS RED L-2817, 0.01 µm to 0.02 µm diameter, available from BASF Inc., anthraquinone pigments such as CROMOPHTAL RED 0.01 µm diameter, CIBA GAIGY Inc., blue colored cobalt aluminate (Al 2 O 3 -CoO) pigments such as COBALT BLUE X, 0.01 µm to 0.02 µm diameter, TOYO-GANRYO Inc., ultramarine colored pigments such as LIONOL BLUE FG-7330, 0.01 µm diameter, TOYO INK Inc., green colored TiO 2 -NiO-CoO-ZnO type pigments such as TYPYROXIDE TM-GREEN #3320, 0.01 µm to 0.02 µm diameter DAINICHI SEIKA Inc., green colored CoO-Al 2 O 3 -Cr 2 O 3 -TiO 2 type pigments such as TYPYROXIDE TM-GREEN #3420, 0.01 µm to 0.02 µm, DAINICHI SEIKA Inc., green colored Cr 2 O 3 type pigments such as ND-801, 0.35 µm diameter, NIHON DENKO Inc., chlorinated phthalocyanine blue pigments such as FASTOGEN GREEN S, 0.01 µm diameter DAINIPPON INK Inc., and brominated phthalocyanine green pigments such as FASTOGEN GREEN 2YK, 0.01 µm diameter, DAINIPPON INK Inc. To the pigment dispersion composition of the present invention, a water-soluble high polymer such as PVA or PVP, a thermosetting resin such as acryl emulsion, or a crosslinking agent such as ADC or diazonium salt may be added, if necessary. According to the second embodiment of the present invention, there is provided a display apparatus comprising a face plate; and a phosphor screen including a pigment layer formed on the inner surface of the face plate, by applying a pigment dispersion composition and a phosphor layer formed on the pigment layer, emitting light of the same color as the color of the pisment itself. The pigment dispersion composition contains 0.5 to 50 parts by weight of an inorganic pigment having a particle diameter of 10 to 200 nm; a dispersant; and water or a solvent miscible with water, characterized in that: said dispersant comprises a mixture of a sodium salt dispersant and an ammonium salt dispersant, or a mixture of an ammonium salt dispersant and nonionic dispersant, said sodium salt dispersant is selected from the group consisting of a sodium salt of an acrylic resin, a sodium salt of an acrylic copolymer resin, a sodium salt of a polycarboxylic acid, and a sodium salt of a condensation product of aromatic sulfonate and formalin, and said ammonium salt dispersant is selected from the group consisting of an ammonium salt of an acrylic resin, an ammonium salt of an acrylic copolymer resin, an ammonium salt of a polycarboxylic acid, and an ammonium salt of a condensation product of aromatic sulfonate and formalin. As heat is applied to the pigment layer mainly during the formation of the phosphor layer, large part of water and dispersant components can be evaporated from the pigment layer. This pigment layer is formed of the pigment dispersion composition of the first embodiment of the invention, which has a good dispersibility, a good transparency and good anti-overcoat properties, and the pigment layer exhibits good filter properties. Further, the pigment dispersion composition has good adhesion properties with respect to a certain part of the substrate while patterning, and good dispersibility. Therefore, it is completely removed from the undesired part of the substrate. According to the second embodiment, the reflection of external light, which takes place between the face plate and the phosphor layer, is suppressed due to a sufficient filter effect of the pigment layer, and the light of a desired color emitting from the phosphor is effectively transmitted. Consequently, the display apparatus according to the second embodiment of the invention has an excellent color purity and a contrast. with pigment dispersion compositions other than the range of the present invention, a pigment layer having such good filter properties cannot be obtained. FIG. 1 illustrates an example of the display apparatus according to the present invention, and is a partial cutaway side view showing a cathode ray tube manufactured on the basis of the invention. A cathode ray tube 60 has an airtight glass envelope 61 the interior of which is evacuated. The envelope 61 has a neck 62 and a cone 63 continuously extending from the neck 62. In addition, the envelope 61 has a faceplate 64 sealed by a frit glass. An explosion-proof tension band 65 consisting of a metal is wound around the periphery of the side wall of the faceplate 64. An electron gun 66 for emitting electron beams is arranged in the neck 62. A phosphor screen 67 is formed on the inner surface of the face plate 64. The phosphor screen 67 is constituted by a phosphor layer which is excited by electron beams from the electron gun 66 to emit light and a pigment layer formed between the phosphor layer and the inner surface of the face plate 64. A deflection unit (not shown) is arranged outside the cone 63. The pigment layer is obtained by applying a pigment dispersion composition containing a 0.5 to 50 parts by weight of an inorganic pigment, at least one kind of dispersant selected from the group consisting of an acrylic resin, an acryl copolymer resin, a polycarbonic acid, and a condensation product of aromatic sulfonic acid and formalin, and water or a solvent miscible with water. The deflection unit serves to deflect electron beams to scan over the phosphor screen. According to the third embodiment of the invention, there is provided a method for manufacturing a display apparatus, said method comprising a process for forming a phosphor screen, consisting the following steps of coating a pigment dispersion composition as mentioned above, on the inner surface of the face plate, and drying to form a coating layer of a pigment dispersion composition; coating a solution containing a photoresist on the coating layer of the pigment dispersion composition to form a coating layer of the photoresist-containing to solution; and exposing the photoresist-containing coating layer to the light via a mask pattern, and then developing thereby patterning the coating layer of the pigment dispersion composition and the coating layer of the photoresist-containing solution at the same time. In the case where phosphor is mixed into a solution containing a photoresist, it suffices if the patterning that is exposure and development steps are carried out for only once each. In such a case, the obtained phosphor layer is calcined at a temperature of, for example, around 430°C after the patterning, thus obtaining a phosphor screen. During the sintering step, much of the dispersants in the coating layers of the photoresist and pigment dispersion composition, and moisture or solvent or the like is evaporated. In the case where a phosphor is not mixed into a solution containing a photoresist, a phosphor slurry containing a photoresist is coated on the inner surface of the face plate after patterning, and then exposed to light via a mask pattern having a predetermined pattern and developed. After that, the resultant is further calcined at a temperature of, for example, around 430°C, thus obtaining a phosphor screen. The display apparatus of the present invention using the above-described phosphor surfaces can be obtained by assembling a display apparatus such as a cathode ray tube, and plasma display by the general method. Next, the present invention will now be described in specific with reference to accompanying drawings. The description will be provided in connection with a color cathode ray tube, taken as a typical example of the display device having a phosphor layer with filter. FIGS. 2A to 2G are schematic views illustrating steps for forming a phosphor screen using the pigment dispersion composition of the present invention. As can be seen in FIG. 2A, a light absorption layer 2 which was patterned is formed on the inner surface of the a face plate 1 of a color cathode ray tube. More specifically, a resist is coated on the inner surface of the face plate 1 of the color cathode ray tube to form a resist film, and the film is exposed to light via a shadow mask (not shown), developed and dried, so as to leave a stripe-like or dot-like photo-curing film in a site 3 in which a phosphor layer is to be formed. On the photo-curing film, a light-absorbing material such as graphite is coated to bind therewith. Then, the photo-curing film is dissolved by cleaning it with a hydrogen peroxide aqueous solution, and thus the photo-curing film is eliminated together with the light-absorbing material integrated thereon. In the above-described manner, there remains to be formed a light-absorbing layer 2 which is patterned to expose the site 3 in which the phosphor layer is to be formed. Accordingly, the cobalt blue as a blue color pigment, the cobalt green as a green color pigment, and the red iron oxide as a red color pigment are used along with pigment dispersion liquids of these colors and a phosphor slurry having a composition later described, and patterning are carried out in order. The patterned films were examined in terms of the development properties, the binding properties with respect to a panel, and the soaking condition. The following embodiments are different from each other in the pigment dispersion composition of each color, and the composition of the phosphor slurry, and these embodiment share the same the pigment layer forming and phosphor layer forming step with that of the embodiment 1. Embodiment 1 (does not fall within the scope of the present invention First, a pigment dispersion composition having the composition listed in TABLE 2 and a phosphor slurry having the composition listed in TABLE 3 were prepared. Pigment dispersion liquids Bp1, Gp1 and Rp1 shown in TABLE 2 were obtained by dispersing the each of the pigments, i.e. the cobalt blue, the cobalt green and red iron oxide separately in SG mills for 60 minutes by using zircon beads having a diameter of 0.8 mm, and adjusting the average diameter to 40 nm. Bp1 Gp1 Rp1 Cobalt blue 20.0g Cobalt green 20.0g Red iron oxide 20.0g Dispeck N-40 3.0g 3.0g 3.0g Pure Water 77.0g 77.0g 77.0g Bs1 Gs1 Rs1 Blue-color emitting fluorescent substance 48.0g Green-color emitting fluorescent substance 48.0g Red-color emitting fluorescent substance 48.0g Polyvinyl alcohol 1.5g 1.5g 1.5g Surfactant 1.0g 1.0g 1.0g Ammonium dichromate (ADC) 1.5g 1.5g 1.5g Pure water 48.0g 48.0g 48.0g Application of the first color As shown in FIG. 2B, the blue color pigment dispersion composition Bp1 is coated to form a coated layer by spin coating on the light-absorbing layer 2 formed on the inner surface of the face plate 1 by patterning, and the coated layer was dried by a heater, thus obtaining a blue color pigment layer 4B. Then, the blue color emitting phosphor slurry Bs1 containing a PVA/ADC resist is coated thereon, thus obtaining a blue color emitting phosphor layer 5B. Next, the blue color emitting phosphor layer 5B and the blue pigment layer 4B were patterned at the same time by exposing them to light via a shadow mask (not shown) for development, and thus a blue color emitting phosphor pixel 6B having a blue color filter as shown in FIG. 2C was obtained. Application of the second color As shown in FIG. 2D, the green color pigment dispersion composition Gp1 is coated on the face plate 1, and the coated composition was dried by a heater, thus obtaining a transparent green color pigment layer 4G. Then, the green color phosphor slurry Bs1 containing a PVA/ADC resist is applied thereon, thus obtaining a green color emitting phosphor layer 5B. Next, the green color emitting phosphor layer 5B was exposed to light via the shadow mask for development, and thus a green color emitting phosphor pixel 6B having a green color filter as shown in FIG. 2E was obtained. Application of the third color As shown in FIG. 2F, the red color pigment dispersion composition Rp1 is coated on the face plate, and the applied composition was dried by a heater, thus obtaining a red color pigment layer 4R. Then, the red color emitting phosphor slurry Rs1 containing a PVA/ADC resist is coated thereon, thus obtaining a red color emitting phosphor layer 5R. Next, the red color emitting phosphor layer 5R was exposed to light via the shadow mask for development, and thus a red color emitting phosphor pixel 6R having a red color filter as shown in FIG. 2G was obtained. By using the face plate thus obtained, a color cathode ray tube was manufactured by the general method, and the properties thereof were evaluated. The results indicated that the color image receiving tube had a good brightness, a good color purity, and a high contrast. Further, the reflection of external light could be reduced by 50% in exchange of a loss of luminescence of only 15%, and the color reproduction area was expanded by 13%. With the conventional technique, for the same external light reflectance as that of the present invention, the loss of brightness is 25% or more and the expansion of the color reproduction area is only 5%, and the films are in some cases defective. As compared to the conventional technique, the color image receiving tube manufactured by using the pigment dispersion composition of the present invention has very much improved properties. Further, in the conventional method, the exposure and development were carried required in the step of patterning a pigment layer to which a photoresist was added, and in the step of patterning a phosphor layer to which a photoresist was added, accordingly, the exposure and development step had to be carried out two times for obtaining one color type of a pixel. However, according to the method of the present invention, the exposure and development can be performed after applying a phosphor slurry on a pigment layer as soon as the pigment layer was formed, and therefore the exposure and development step should be carried out only once for obtaining one color type of a pixel. Consequently, with the method of the present invention, the exposure and development step should be repeated only three times in order to obtain three colors of pixels comparing that the conventional method requires at least six times of these steps. Thus, the manufacture of a color image receiving tube can be simplified by the present invention. If a conventional pigment dispersion composition is applied to the method of the present invention, part of the pigment layer is soaked into the phosphor layer, deteriorating not only the filter effect of the pigment layer, but also the light emitting efficiency of the phosphor layer. When the pigment dispersion composition of the present invention is used, part of the pigment layer is not soaked into the phosphor layer, and therefore a good filter effect can be achieved and the light emitting efficiency is not degraded. Embodiment 2 (does not fall within the scope of the present invention) The above embodiment 1 is a case where only Dispeck N-40, which is an anionic Na salt dispersant, was used as a dispersant for the pigment dispersion composition, whereas the second embodiment, which will now be described, is the case where only Dispeck A-40, which is an anionic NH 4 salt dispersant, was used. This embodiment involves the same method and the phosphor slurry as those of the first embodiment except that the pigment dispersion composition has the composition listed in TABLE 4. Bp2 Gp2 Rp2 Cobalt blue 20.0g Cobalt green 20.0g Red iron oxide 20.0g Dispeck A-40 3.0g 3.0g 3.0g Pure Water 77.0g 77.0g 77.0g By using the face plate thus obtained, a color cathode ray tube was manufactured, and the properties thereof were evaluated. The results indicated that the color cathode ray tube had a good brightness, a good color purity, and a high contrast. Further, the reflection of external light could be reduced by 50% in exchange of a loss of luminescence of only 7%, and the color reproduction area was expanded by 15%. Although the second embodiment exhibited slightly better characteristics than those of the first embodiment, the second embodiment involves slightly more detects in removing of the pigment at non-exposed part than the first embodiment to remain some residue. Embodiment 3 The first and second embodiments are directed to the case where the anionic Na salt or anionic NH 4 salt is solely used in the pigment dispersion composition as a dispersant; however the third embodiment will be described in connection with a case where two types of dispersants are mixed. This embodiment involves the same method and the phosphor slurry as those of the first embodiment except that the pigment dispersion composition has the composition of Bp3, Gp3 and Rp3, as listed in TABLE 5. Bp3 Gp3 Rp3 Cobalt blue 20.0g Cobalt green 20.0g Red iron oxide 20.0g Dispeck N-40 2.1g 2.1g 2.1g Dispeck A-40 0.9g 0.9g 0.9g Pure Water 77.0g 77.0g 77.0g By using the face plate thus obtained, a color cathode ray tube was manufactured, and the properties thereof were evaluated. The results indicated that the color cathode ray tube had a good brightness, a good color purity, and a high contrast. Further, the reflection of external light could be reduced by 50% in exchange of a loss of luminescence of only 7%, and the color reproduction area was expanded by 15%. The second embodiment exhibited a high yield. Embodiment 4 The fourth embodiment is similar to the third embodiment except that the mixed ratio of the anionic Na salt and anionic NH 4 salt was varied. The pigment dispersion composition and the composition of the phosphor slurry used in the fourth embodiment were as shown in TABLES 6 and 7. Bp4 Gp4 Rp4 Cobalt blue 20.0g Cobalt green 20.0g Red iron oxide 20.0g Dispeck N-40 2.4g 2.4g 2.4g Dispeck A-40 0.6g 0.6g 0.6g Pure Water 77.0g 77.0g 77.0g Bs4 Gs4 Rs4 Blue-color emitting fluorescent substance 48.0g Green-color emitting fluorescent substance 48.0g Red-color emitting fluorescent substance 48.0g Polyvinyl alcohol 1.4g 1.4g 1.4g Surfactant 1.0g 1.0g 1.0g Ammonium dichromate 1.6g 1.6g 1.6g Pure water 48.0g 48.0g 48.0g The fourth embodiment exhibited the same results as those of the third embodiment. Embodiment 5 The fifth embodiment is similar to the third embodiment except that the mixed ratio of the anionic Na salt and anionic NH 4 salt was varied. The pigment dispersion composition and the composition of the phosphor slurry used in the fifth embodiment were as shown in TABLES 8 and 9. Bp5 Gp5 Pp5 Cobalt blue 20.0g Cobalt green 20.0g Red iron oxide 20.0g Dispeck N-40 2.5g 2.5g 2.5g Dispeck A-40 0.5g 0.5g 0.5g Pure Water 77.0g 77.0g 77.0g Bs5 Gs5 Ps5 Blue-color generating fluorescent substance 48.0g Green-color generating fluorescent substance 48.0g Red-color generating fluorescent substance 48.0g Polyvinyl alcohol 1.5g 1.5g 1.5g Surface active agent 1.0g 1.0g 1.0g Ammonium dichromate 1.5g 1.5g 1.5g Pure water 48.0g 48.0g 48.0g The sixth embodiment exhibited the same results as those of the third embodiment. As described in the above embodiments 3 to 5, in the case where the mixed ratio between the anionic Na salt and anionic NH 4 salt was changed, the PVA/ADC ratio in the phosphor slurry was also changed. Embodiment 6 The sixth embodiment in which a mixture of the anionic NH 4 salt dispersant and nonionic dispersant was used, will be described. The pigment dispersion composition and the composition of the phosphor slurry used in the sixth embodiment were as shown in TABLES 10 and 11. Bp6 Gp6 Pp6 Cobalt blue 20.0g Cobalt green 20.0g Red iron oxide 20.0g Dispeck N-40 2.94g 2.94g 2.94g Dispeck A-40 0.06g 0.06g 0.06g Pure Water 77.0g 77.0g 77.0g Bs6 Gs6 Ps6 Blue-color generating fluorescent substance 48.0g Green-color generating fluorescent substance 48.0g Red-color generating fluorescent substance 48.0g Polyvinyl alcohol 1.6g 1.6g 1.6g Surface active agent 1.0g 1.0g 1.0g Ammonium dichromate 1.4g 1.4g 1.4g Pure water 48.0g 48.0g 48.0g The sixth embodiment exhibited the same results as those of the third embodiment. The above embodiments were described in connection with a color cathode ray tube; however the present invention can be applied to those utilizing the light emission of a phosphor. Further, the pigment dispersion liquid of the present invention is very advantageous in the case where an appropriate adhesion and an appropriate separability with respect to a glass substrate are required at the same time, and can be applied to various cases apart from the manufacture of a display apparatus. Embodiment 7 Any of above embodiments perform the patterning step after a pigment layer and a phosphor layer are coated. However, according to the present invention, the patterning step can be performed after a pigment layer and a photoresist layer are coated without phosphor. More excellent phosphor screen can be obtained in this case although patterning times for forming a phosphor screen may be increased. Generally, a photoresist is mixed in a pigment dispersion in a conventional method of forming a pigment layer. However this pigment layer has a problem which transparency of the pigment layer is decreased due to much photoresist mixed in the pigment dispersion in order to make high photosensitivity. In this embodiment, a step for patterning a photoresist layer together with a coating layer of a pigment dispersion composition according to the present invention is very useful because the pigment dispersion layer need not to contain a photoresist. The seventh embodiment is following. A pigment dispersion composition was prepared according to TABLE 5. A photoresist solution was prepared according to TABLE 3 except for a phosphor component was removed. A phosphor slurry was prepared according to TABLE 3. First, a blue pigment layer was formed by applying a blue pigment dispersant liquid Bp3. A photoresist solution is coated on the pigment layer and then exposing and developing to form a patterned blue pigment layer. The similar forming steps was repeated except for using red pigment, and green pigment, expectively, to form a red pigment layer and a green pigment layer. Next, the phosphor layer was formed on these pigment layers by using a conventional method to form a phosphor screen with a filter. The pigment layer formed as described above has a good patterning property. As result display properties of a display using the pigment layer becomes good.

Claims: A pigment dispersion composition containing: 0.5 to 50 parts by weight of an inorganic pigment having a particle diameter of 10 to 200 nm; a dispersant; and water or a solvent miscible with water, characterized in that: said dispersant comprises a mixture of a sodium salt dispersant and an ammonium salt dispersant, or a mixture of an ammonium salt dispersant and nonionic dispersant, said sodium salt dispersant is selected from the group consisting of a sodium salt of an acrylic resin, a sodium salt of an acrylic copolymer resin, a sodium salt of a polycarboxylic acid, and a sodium salt of a condensation product of aromatic sulfonate and formalin, and said ammonium salt dispersant is selected from the group consisting of an ammonium salt of an acrylic resin, an ammonium salt of an acrylic copolymer resin, an ammonium salt of a polycarboxylic acid, and an ammonium salt of a condensation product of aromatic sulfonate and formalin. A pigment dispersion composition according to claim 1, characterized in that a content of said dispersant is 0.5 to 20 wt%. A pigment dispersion composition according to claim 1, characterized in that a content of said dispersant with respect to said inorganic pigment is 2 to 30 wt%. A pigment dispersion composition according to claim 1, characterized in that said solvent miscible with water is at least one kind selected from the group consisting of methyl alcohol, ethyl alcohol, isopropyl alcohol, polyhydric alcohols, glycolethers, 2-pyrrolidone, N-methylpyrrolidone and N,N-dimethylformamide. A pigment dispersion composition according to claim 1, characterized in that said nonionic dispersant is selected from the group consisting of polyoxyethylene laurylether, polyoxyethylene derivatives, polyoxyalkylene alkylether, polyoxyethylene nonylphenylether, and polyoxyethylene sorbitanmonolaurate. A pigment dispersion composition according to claim 1, characterized in that said dispersant is a mixture of a sodium salt of an acrylic resin and an ammonium salt of an acrylic resin. A pigment dispersion composition according to claim 1, characterized in that a content of said inorganic pigment is 3 to 35 wt%. A display apparatus (60) characterized by comprising: a face plate (64); and a phosphor screen (67) comprising a pigment layer (4B, 4G, 4R), and a phosphor layer (5B, 5G, 5R), formed on the pigment layer (4B, 4G, 4R), emitting light of the same color as the color of the pigment itself, characterized in that said pigment layer (4B, 4G, 4R) is formed by applying a pigment dispersion composition according to claim 1 on the inner surface of the face plate (64). A display apparatus (60) according to claim 8, characterized in that a content of said dispersant is 0.5 to 20 wt%. A display apparatus (60) according to claim 8, characterized in that a content of said dispersant with respect to said inorganic pigment is 2 to 30 wt%. A display apparatus (60) according to claim 8, characterized in that said solvent miscible with water is at least one type selected from the group consisting of methyl alcohol, ethyl alcohol, isopropyl alcohol, polyhydric alcohols, glycolethers, N-methylpyrrolidone, 2-pyrrolidone and N,N-dimethylformamide. A display apparatus (60) according to claim 8, characterized in that said nonionic dispersant is selected from the group consisting of polyoxyethylene laurylether, polyoxyethylene derivatives, polyoxyalkylene alkylether, polyoxyethylene nonylphenylether, and polyoxyethylene sorbitanmonolaurate. A display apparatus (60) according to claim 8, characterized in that said dispersant is a mixture of a sodium salt of an acrylic resin and an ammonium salt of an acrylic resin. A display apparatus (60) according to claim 8, characterized in that a content of said inorganic pigment is 3 to 35 wt%. A method of manufacturing a display apparatus (60), said method comprising a process for forming a phosphor screen, characterized by comprising the steps of: coating a pigment dispersion composition according to claim 1 on the inner surface of the face plate (64), and drying, thereby forming a coating film (4B, 4G, 4R) of a pigment dispersion composition; coating a solution containing a photoresist on the coating film of the pigment dispersion composition, thereby forming another coating film (5B, 5G, 5R) of the photoresist solution; and exposing and developing the coating film (5B, 5G, 5R) of the photoresist solution via a mask pattern, thereby patterning the coating film (4B, 4G, 4R) of the pigment dispersion and the coating film (5B, 5G, 5R) of the photoresist solution at the same time. A method according to claim 15, characterized in that said solution containing said photoresist further contains a phosphor. A method according to claim 15, characterized in that a content of said dispersant is 0.5 to 20 wt%. A method according to claim 15, characterized in that a content of said dispersant with respect to said inorganic pigment is 2 to 30 wt%. A method according to claim 15, characterized in that said solvent miscible with water is at least one type selected from the group consisting of methyl alcohol, ethyl alcohol, isopropyl alcohol, polyhydric alcohols, glycolethers, 2-pyrrolidone, N-methylpyrrolidone and N,N-dimethylformamide. A method according to claim 15, characterized in that said nonionic dispersant is selected from the group consisting of polyoxyethylene laurylether, polyoxyethylene derivatives, polyoxyalkylene alkylether, polyoxyethylene nonylphenylether, and polyoxyethylene sorbitanmonolaurate. A method according to claim 15, characterized in that said dispersant is a mixture of a sodium salt of an acrylic resin and an ammonium salt of an acrylic resin. A method according to claim 15, characterized in that a content of said inorganic pigment is 3 to 35 wt%.

Inventors: CHIGUSA HISASHI, FUKUDA MASARU, ITOU TAKEO, MATSUDA HIDEMI, SAKAI KAZUO, CHIGUSA, HISASHI, FUKUDA, MASARU, ITOU, TAKEO, MATSUDA, HIDEMI, SAKAI, KAZUO
Applicants: FUJI PIGMENT, TOSHIBA KK, FUJI PIGMENT CO., LTD., KABUSHIKI KAISHA TOSHIBA
Application year: 1994
Main classification: C09D17
IPC codes: H01J29, C09D17